1. Field of the Invention
This invention relates to microscopy, optical imaging, adaptive optics, computer image processing, and computer-aided tomography.
2. Description of the Prior Art
Light waves interact with a microscopic specimen to form a transform of optically accessible elements. This transform simultaneously bears spatial information from all visible areas of the specimen with an elemental, or distinguishable pixel, size to 1/4 of the wavelength of light in the surrounding medium. A conventional microscope objective phasally retransforms the wavefront to cause convergence onto a two-dimensional sensor, such as a film, vidicon, the human retina, or in a reciprocal relationship a flying-spot scanner CRT, forming a representation of the original specimen with elemental clarity proportional to the cosine of the half-angle with which the objective encompasses the element, and depth clarity inversely related to that angle. Large numerical aperture (N.A.), optically perfect, objectives ultimately approach the 1/4 wave limit mentioned above at complete cutoff, or 0% modulation transfer, with a Rayleigh limit 1.22 times this size, and with however still less than 50% transfer at twice the size, or equivalently half the cutoff spatial frequency, giving a "soft focus" effect. This highest resolution is obtained at the expense of the narrowest depth of field, less than half the wavelength of light axial to the lens, precluding the viewing of dimensional relationships. To regain some depth of focus, a smaller N.A. objective is used, with proportionally less resolution. Yet the need for depth clarity is such that these "low power" objectives usually are considered the most useful.
By utilizing the extremely short De Broglie waves of moderate speed electrons, the scanning electron microscope permits a wide depth of focus comparable in appearance to macro-photography, and therefore is often used even for magnifications below 3,000.times. of dimensional specimens which light as a transform would be capable of imaging if retransformation technology were available. A disadvantage of electron microscopy is the requirement of a vacuum, and corollary dehydration and cellular breakdown caused by boiling or sublimation, preventing almost all life forms from being viewed in vivo, and preventing many structurally delicate life forms from being directly viewed at all. Of course an electron microscope can not image natural color.
Depth of focus has been extended in the prior art by "integrated focusing" in which the focus is changed, with a special objective that prevents magnification variance, during an exposure of a single image. The result is a very soft image with, however, some detail from several planes. A modification of this technique projects the illuminating light in a plane which is moved with the plane of focusing; however, this is primarily limited to opaque, convex objects with no concave pockets, and also to low magnifications and viewing angles, as light can not be confined to a plane one wavelength thick over a width of more than one wavelength.
Classical x-ray tomography uses a moving source and film to introduce a limited depth of field to a normally "infinite" depth of field x-ray system, the reverse of the goals of micro-optical tomography. Computer-aided-tomography (CAT) mathematically dissects a subject from a set of one-dimensional scans at varying angles, a 2-D to 2-D transformation. Because opaque reflection imaging and the limiting optical features of diffraction, focus, and depth of field do not exist in macro x-ray work, CAT and micro-optical tomography are substantially different technologies.